Bags having the configuration of the bags produced by the subject matter of the present invention are generally referred to as "T shirt bags". The construction essentially comprises the creation of inwardly directed folds or gussets in tubular web material which is sealed and cut at regularly spaced intervals to produce an envelope or a pillow having each end heat sealed.
Some existing procedures transport the envelope to a stacking station which may include upstanding members, such as fences, to accumulate successive gusseted and sealed envelopes to create a stack. Once the stack is completed, it is manually removed by the operator and further processed by a press having a knife shaped to remove a generally rectangular portion from the stack of web segments. The knife cuts through the stack of web segments such that the inner extremity of the gussets and a portion of one of the transverse seals is severed, thereby creating loops which can be grasped by hand or receive the forearm of a user.
The above procedure involves certain disadvantages which relate to stack registration meaning that the corresponding edges of successive bags or web segments overlie each other so that the completed stack takes the form (much like a ream of paper or a deck of cards), the labor and time involved for manual removing and placing the stacks in machinery which effects cutting of the generally rectangular slug and the finished stacks do not easily lend themselves for cartoning in an organized fashion.
Methods and machinery are presently available for improving stack registration by interconnecting the web segments along the trailing or leading edge to maintain stack registration during manual pickoff and punching. Two known approaches are used. One involves providing heated pins or bars located adjacent the sealing station that are effective to tack weld or block the stack as it is being generated. The second approach involves a heated bar in contact with one marginal edge of the welded web segments to unify the successive segments as a stack is being created. To effect this association of web segments tack welding sometimes is restricted to the area of the bag edge which will be punched or cut out when the final stage of producing a T shirt bag is accomplished.
Certain approaches extend the tacking area of the successive bags along the entire margin of the web segment so that even after removing a rectangular segment, all of the bags are unified along the remaining edge portions. Whether heated pins are used or a heated blocking bar, the manual operation of removing the bag stack from the stacking table to the punching machine requires manual effort in removing the unified or blocked stack of bags from the bag making machine to the punching unit.
To eliminate labor costs associated with removing bag stacks from the line and improve quality, T shirt bag operations have resorted to cutting the rectangular segment from the stack of web segments on the bag machine.
Further improvements have resulted in machinery in which removal of the generally rectangular portion occurs as each web segment is produced by the bag making machine and thereafter folding the individual T shirt bag before stacking. The beneficial effects of this approach include reduction of stack dimension and the elimination of problems attendant with the extended grasping loops. As a result stack handling, cartoning and dispensing was considerably improved.
In producing the cutout of the individual bags on the bag machine certain problems, principally dealing with control of the web segment and the utilization of a shaped cutting blade propelled by pneumatic cylinders arose. Removal of the rectangular section from the web before sealing produced serious wrinkling problems which diminished the quality and accordingly the acceptability of the resulting T shirt bag. Moreover, punching or severing the generally rectangular slug from the web tube before sealing and severing required extreme accuracy in order to avoid the creation of slits or slight cuts in the bottom seal. Accuracy of this magnitude is not repetitively possible and to utilize this approach required more web for each bag.
The present state of the art incorporates rotary dies downstream of the seal bar to produce the rectangular cut-outs. This approach does fulfill the requirements of a high quality bag (one in which the rectangular cut-out is cleanly made and accurately positioned) but the rotary dies and the machine elements supporting and rotating the dies are exceedingly expensive to insure proper continuous operation and on changing bag size, replacement of the rotary dies is an expensive alteration.